More particularly, the embodiments of the present invention relates to an optical proximity sensor adapted to be mounted in a liquid-jet instrument having a spray head for spraying of jet of liquid, the optical senor serving to evaluate a distance between it and a given surface onto which the liquid is to be sprayed.
French Patent Application FR 2 841 498 describes, in particularly, a writing instrument that includes such an optical sensor which can, for example, be formed by an infrared light-emitting diode (LED) which sends an incident light beam towards the given surface so as to form a light spot on said given surface and a reflected light beam which is then received, for example, by a photodiode which then issues a signal representing the reflected light beam. The signal representing the reflected light beam is then analyzed by a processor unit in order to evaluate the distance between the optical sensor and the given surface in order to trigger or not to trigger activation of the liquid spray head so as to spray or not spray a certain quantity of liquid onto the given surface, such as a writing surface.
In known writing instruments, the light-emitting element of the optical sensor can be mounted in the writing instrument anywhere that is in the vicinity of the spray head, and the light-receiving element is also mounted on any support that can be different while also being situated in the vicinity of the spray head. It can thus be understood that mounting the various light-emitting and light-receiving elements one after another complicates mounting the optical sensor as a whole on the liquid-jet instrument without being certain that the light-emitting and the light-receiving elements are always in the same relative positions. That uncertainty as to the relative positions of the light-emitting and of the light-receiving elements can give rise to errors in evaluating the distance between the optical sensor and the given surface, which also modifies the sensitivity of the optical sensor from one liquid-jet instrument to another.